Cavendish experiment, in which the attraction of lead balls of known mass is measured by means of a torsion balance, and so compared with the attraction of the earth; and the Schiehallion experiment, in which a plumb line is suspended near a mountain of known mass, and the deflection of the line from the vertical carefully measured. But both experiments proceed upon the assumption that all matter attracts, and prove nothing.
This review of the Newtonian conception serves as a preface to the authors' own theory, which is a direct outgrowth from the four primary principles deduced in an earlier book persistence, resistance, reciprocity, and equalization. Briefly stated, their theory is that two bodies in different states of excitation and free to move will move toward each other, the intensity of attraction being proportional to the difference in the excitation. Bodies in the same state—that is, in equilibrium—have no attraction for one another, and there will be no gravitation manifested between them. This is a direct contradiction of the Newtonian position that gravitation is universal. The excitation of a body may be increased by heat, light, electricity, or magnetism, and consequently the attraction, weight, or mass may be changed by a change in the physical conditions. This has been repeatedly shown by experiment, but with the idea of the unchangeableness of gravity firmly fixed in the mind the results of the experiments have always been explained on other grounds. According to the new view, terrestrial gravitation is entirely due to the different states of excitation which prevail on the outside of the globe and on the inside, and notably to the difference in thermal condition. Heating a body on the surface of the earth ought, by lessening this difference, to reduce the attraction—that is to say, the weight—and such is actually the case. Every one who has worked in the laboratory knows that a hot platinum crucible weighs several milligrammes less than the same crucible when cold. This was formerly attributed to ascending currents of hot air, but the explanation no longer holds. These and other similar experiments have recently been repeated under conditions which do not admit the existence of convection currents, and the loss of weight is still observable.
With permission we quote from a letter recently received from Mr. Paul R. Heyl, of Philadelphia: "I have been making a curious experiment since I got back within reach of an analytical balance. I took a piece of three-quarter-inch glass tubing, sealed it at one end, and choked it slightly about one inch from the sealed end. In the lower chamber thus formed I placed dilute sulphuric acid, and dropped in a piece of solid caustic potash, which was arrested at the choke. I then sealed off the upper end of the tube about two inches above the choke. This arrangement I then
